Step-down transformers come in 2 shades= a series winding with tapping's[auto] or an isolated primary and secondary transformer .The first while supplying instant current are dangerous as you are directly connected to the mains.

The isolated version is safer but must be able to supply the peak voltage required as in a powerful Hi-Fi amp so must be high current or you would get clipping.due to voltage /current limitations.

On an "auto" transformer there should be voltage tappings marked. A standard MAINS ISOLATED[primary/secondary windings] are usually set at one drop -down voltage.

Yes you can get unusual set ups but I am talking of your "standard" definition version.